This proposal is concerned with a study of the biosynthesis of penicillin and cephalosporin antibiotics. Some of the specific questions to be answered are: 1) Is delta (L- aminoadipyl)-L-cysteinyl-D-valine a key biosynthetic intermediate? 2) At what stage does the alpha-aminodipic acid and valine moieties invert to the D-configuration? 3) Is the beta-lactam ring formed prior to the thiazolidine and dihydrothiazine rings or vice versa - formation of a seven or eight-membered ring respectively, followed by contraction? 4) At what point of biosynthetic pathway does penicillin N and Cephalosporin C diverge? Are these beta-lactam antibiotics derived from a common tripeptide intermediate? Various structural analogs of amino acids will be made with a view to produce "dead-end" intermediates. Also several potential penultimate precursors will be synthesized and evaluated for their biosynthetic intermediacy.